1. Field of the Invention
The present invention relates to a variable flow valve mechanism configured to open and close an opening of a gas passage to achieve a variable flow rate of an exhaust gas to be supplied to a turbine wheel side in a vehicle turbocharger.
2. Description of the Related Art
A bypass passage (one of gas passages) is usually formed inside a turbine housing of a vehicle turbocharger as a measure for preventing an excessive rise in boost pressure caused by the vehicle turbocharger. The bypass passage causes part of an exhaust gas to bypass a turbine wheel (turbine impeller). In other words, the bypass passage renders a flow rate of the exhaust gas to be supplied to the turbine wheel side variable. A waste gate valve (one of variable flow valve mechanisms) is provided at an appropriate position of a gas passage or the turbine housing. The waste gate valve opens and closes an opening of the bypass passage. A general configuration and other factors of the waste gate valve are as follows.
A stem is rotatably supported by a support hole that is formed to penetrate through an outer wall of the turbine housing. A base end portion (one end portion) of the stem projects to the outside of the turbine housing. A link member is integrally provided at the base end portion of the stem. The link member is driven by an actuator to swing in forward and reverse directions around the center axis of the stem.
An attachment member is integrally provided at a tip end portion (the other end portion) of the stem. An attachment hole is formed to penetrate through the attachment member. In addition, a valve is provided fitted into the attachment hole in the attachment member. The valve is allowed to have backlash (move and swing) on the attachment member. In the meantime, the valve includes a valve body capable of coming into contact with and separating from a valve seat on the opening side of the bypass passage, and a valve shaft integrally formed at the center of the valve body and fitted into the attachment hole in the attachment member. Here, the valve body remains in contact with the valve seat on the opening side of the bypass passage until a pressure on an outlet side of a compressor wheel (compressor impeller) of the vehicle turbocharger reaches a preset pressure. In this state, a follow-up performance (sealing performance) of the valve body to the valve seat on the opening side of the bypass passage is secured by allowing the valve to have the backlash on the attachment member. Furthermore, a washer serving as a clasp for preventing the valve from being separated from the attachment member is integrally provided at a tip end portion of the valve shaft.
Accordingly, when the pressure on the outlet side of the compressor wheel reaches the preset pressure while the vehicle turbocharger is in operation, the link member is driven by the actuator to swing in the forward direction (one direction) and thus to rotate the stem in the forward direction. Thereby, the valve is caused to swing in the forward direction and the valve body is separated from the valve seat on the opening side of the bypass passage. In this way, the waste gate valve opens the opening of the bypass passage to cause part of the exhaust gas to bypass the turbine wheel, and thereby to enable reduction of the flow rate of the exhaust gas to be supplied to the turbine wheel side.
On the other hand, when the pressure on the outlet side of the compressor wheel falls below the preset pressure, the link member is driven by the actuator to swing in the reverse direction (the other direction) and to thus rotate the stem in the reverse direction. Thereby, the valve is caused to swing in the reverse direction, and the valve body is brought into contact with the valve seat on the opening side of the bypass passage. In this way, the waste gate valve closes the opening of the bypass passage, and can be returned to the original state.
Japanese Patent Application Laid-Open Publications Nos. 2009-236088 and 2008-101589 disclose the related art to the present invention.